Modern cars are equipped with air cushion restraint systems which deploy to protect occupants in the event of a vehicle crash. A driver's side restraint system includes an airbag which deploys from the steering wheel hub, and the passenger's side restraint system includes a larger airbag which deploys from the dashboard of the vehicle. Both the driver's side and passenger's side airbag cushion restraint systems often include hybrid inflators for providing inflation gasses to the airbag. The hybrid inflators include a compressed gas and a combustible material which provides heat and additional inflation gas augmenting the volume and pressure of the stored compressed gas.
The performance of the airbag occupant restraint systems, and particularly the larger size passenger's side airbag, is preferably optimized as a function of variables associated with each particular crash. These variables include the severity of the crash and also include the size and position of the passenger as well as temperature conditions that may affect the performance of the inflator. For instance, the least aggressive deployment of the airbag is appropriate for a low speed crash with an out-of-position, small occupant, wherein the most aggressive deployment of the airbag may be appropriate for a head on high-speed crash with a large adult passenger. The inflation of the bag is, of course, in large part controlled by the operation of the inflator.
Previous efforts at adjusting the performance of a hybrid inflator have centered about operating the hybrid inflator in stages through its primary gas delivery outlet. For instance, in some instances a variable time delay between release of the compressed gas and ignition of the combustible material for augmenting the pressurized gas has been provided. In other instances, the combustible material has been provided in multiple or staged combustible units, with means for controlling the number of stages operated in a particular crash. An airbag restraint system has also been provided with a diffuser which vents a portion of the gas away from the airbag, after the gas has been released through the vent outlet.
Modern vehicles are increasingly being equipped with additional auxiliary airbag systems, such as knee bolsters and side impact airbags. Discreet inflators are usually provided for each of these systems. These additional restraint systems are generally inflated before the large passenger side airbag, in that the distance between the occupant's knees and the knee bolster or the distance between the occupant's shoulders and the side of the vehicle are small, necessitating a fast response. It would be advantageous if a single inflator could be adapted to provide inflation for the primary airbag cushion and to one or more additional airbag cushions as well.